NEUTRILIZING CHLORINE
From: ausprawnfarms@hotmail.com
Date: 28 September 2001
QUESTION:
We are a new
prawn farm in Australia and have been using sodium
thiosulphate to neutralize chlorine for sterilization. We were wondering if
anyone knew of an alternative chemical that is used for this process that is
readily available and safe to use for crustaceans.
Matt West &
Scott Walter
e-mail : ausprawnfarms@hotmail.com
***************
COMMENTS 1 :
If your water
volumes are not too large, try cheap, soluble vitamin C. It will not only
neutralize the chlorine, but the shrimp may benefit from the residuals. This
is a trick used by hatchery operators, but may not be economical for ponds.
Henry C. Clifford
Technical Director
Super Shrimp Group
e-mail: Hcclifford@aol.com
***************
COMMENTS 2 :
Sodium
thiosulphate is o.k. to use on crustaceans at low levels but at
high levels 100 mg/L or higher can cause mortalities in some larvae. I found
that a problem with larval Macrobrachium rosenbergii. I'm not sure how it
affects juveniles and adults. You can use it as long as you minimize its use
and don't let it accumulate in the tanks. I'm not sure at what levels you're
chlorinating and therefore the levels of sodium thiosulphate being used. At
low levels, you can simply let the chlorine dissipate.
Bill Daniels
Research Associate Professor/
Extension Specialist, Aquaculture
Delaware State University
Dover, DE 19901-2277, USA
E-mail: wdaniels@dsc.edu
***************
COMMENTS 3:
What about the
dosage for vit. C to neutralize e.g. 1 g active chlorine?
Gerrit Quantz
e-mail: butt.fischfarm@t-online.de
***************
COMMENTS 4 :
Have you tried
circulating the water through an activated carbon chamber? This will
certainly remove chlorine and dissolved organics while adding nothing to the
culture water.
Howard W.
Newman
Desert Lake Technologies, LLC
e-mail: bshrimp@aol.com
***************
COMMENTS 5:
It takes about
10 ppm of ascorbic acid to inactivate 1 ppm of chlorine. Beware of use in
larval shrimp as some toxicity problems have been reported at high levels.
Stephen G. Newman Ph.D.
President
Aqua-In-Tech Inc.
6722 162nd Place SW
Lynnwood, WA 98037, USA
Tel: 425-787-5218
Fax: 425-741-0857
e-mail: sgnewm@aol.com
URL : http://www.aqua-in-tech.com
***************
COMMENTS 6 :
Rather than
inadvertently misleading you with inaccurate information about treatment
levels, start with 5-10 ppm Vit. C. in your reservoir, and then check for
chlorine residuals with orthotoluidine (or a suitable alternative).
Toxicity levels depend on what developmental stage of shrimp you are
culturing. Obviously larvae would be more sensitive than juveniles or
adults. Also, it depends on how much water exchange you are going to make
from the reservoir. More than 10 ppm might be toxic to larvae (as Dr. Newman
points out), but if you are going to use the water stored (and treated) in a
reservoir for only a 25% exchange, you could (hypothetically) apply 40 ppm
of Vit. C in the reservoir, and still be within acceptable limits. Some of
the Vit. C will also be "neutralized" by algae and bacteria in the
culture water.
If you have the luxury of time on your side, vigorous aeration is usually
the best means of ridding your water of chlorine residuals.
Henry Clifford
e-mail: hcclifford@aol.com
***************
COMMENTS 7 :
I would also
like to submit a question about dechlorination. We are an
aquaculture research facility, using 2 independent dechlorination units
for our fresh water. The units have been designed to required
specifications (containing active carbon - charcoal over two grades of
gravel) and have been performing well over the past 9 years. Biannual
analysis of substrate core samples for % remaining carbon activity has
always been done. For the first four years, up until 1996, the % carbon
activity had been decreasing gradually, as the total flow through water
volume increased. When the % carbon activity fell under 10 %, we changed the
substrate in 1996. Since then, the % carbon activity sampling results have
been puzzling. The new substrate had an initial activity level of around 50
% in both units. Over the past five years, our fresh water requirements have
been constant, but greater than in the preceeding period. However, the
% carbon activity of the core samples has remained the same. It has
been fluctuating between 40 and 45 % for both units since 1998. We adjusted
our sampling to compare results before and after backwashing of the
dechlorination units, since I have been told that backwashing may
temporarily increase carbon activity. This did not seem to make a
difference. Sample analysis has always been done by the same
accredited laboratory. My question : is it possible that the
results would be the same over such a long period? Does anyone know
whether the % carbon activity decreases at a linear rate? We are
concerned that we are missing something and that the results may somehow not
be reliable. Any thoughts or suggestions would be appreciated.
Does anyone have the coordinates of an expert in the field?
Simona Motnikar
e-mail: simona.motnikar@agr.gouv.qc.ca
***************
COMMENTS 8 :
The treatment
of culture water is the most important step in aquaculture. Chlorination is
probably the simplest method for sterilization and is best for very
large cultures. If chlorination used dry chlorine mixtures containing
calcium hypochlorite, it is not as good as those containing sodium
dichloro-s-triazinetri-one dihydrate. If aeration is heavy for 12-24 hr, it
is usually not necessary to dechlorinate
with sodium thiosulfate (reference).
Ismawi B. Ramli
e-mail: ismawie_r@yahoo.com